High-definition (HD) video signals typically require a high-definition television or other devices in order to be viewed. With an aspect ratio of 16:9 (1.78:1), HD video approaches current aspect ratios of regular widescreen film recorded at typically 1.85:1 or 2.40:1 (sometimes traditionally quoted at 2.35:1). Standard-definition (SD) video differs from HD video by having an aspect ratio of 4:3 (1.33:1). Numerous video standards and formats have emerged to output HD and SD video. However, each format presents unique characteristics and specifications. As such, decoding and encoding digital video can be limited by processing capabilities of video processing systems to support either one standard or the other.
Moreover HD video requires a significantly greater processing capability than SD because of HD's higher resolution. Video processing is typically carried out on macroblocks. A macroblock is a group of spatially adjacent pixels, usually forming a rectangular block, processed more or less together and somewhat separately from other pixels. An SD video system has a resolution of 720 by 480 pixels at a frame rate of 30 frames per second (fps). Thus for a macroblock having 256 pixels, an SD system requires 1,350 macroblocks to be processed per frame and a total of 40,500 macroblocks to be processed per second. On the other hand, HD has a resolution of 1920 by 1080 pixels, which becomes 1920 by 1088 when rounding 1080 up to the nearest number divisible by 16, and thus for a macroblock of 256 pixels, an HD system requires 8,160 macroblocks to be processed per frame and a total of 244,800 macroblocks to be processed per second. These different processing requirements make it difficult to design a common video processing architecture that will be useful in processing both SD and HD signals and with sufficient processing power for HD systems.